Aldehyde cationic derivatives of galactose containing polysaccharides used as paper strength additives

ABSTRACT

Aldehyde cationic derivatives of galactose containing polysaccharides which are obtained by oxidizing galactose containing polysaccharides with the enzyme galactose oxidase. The enzyme oxidized products have an aldehyde function at a specific position of the polysaccharide, i.e., the C 6  position, of the galactose unit, and the cationic derivatives thereof have unexpected and significantly improved properties when used as paper strength additives.

This application is a division of application Ser. No. 08/426,808, filedApr. 21, 1995, now U.S. Pat. No. 5,554,745 which is a continuation ofapplication Ser. No. 08/883,319 filed May 14, 1992 and now abandoned.

BACKGROUND OF THE INVENTION

This invention relates to novel aldehydic, cationic derivatives ofnatural occurring galactose containing polysaccharides obtained bysite-specific oxidizing the selected polysaccharide with the enzymegalactose oxidase. This cation derivatized, enzyme oxidized product hasan aldehyde function at a specific position of the polysaccharide andprovides surprising strength properties when used as a paper additive.

The term "paper" as used herein includes sheet-like masses and moldedproducts made from cellulosic materials which may be derived fromnatural sources as well as from synthetics such as polyamides,polyesters and polyacrylic resins and from mineral fibers such asasbestos and glass. In addition, papers made from combinations ofcellulosic and synthetic materials are applicable herein. Paperboard isalso included within the broad term "paper".

The modification of starch and other polysaccharides by many differentmethods to produce various cation and aldehyde containingpolysaccharides as well as cationic-aldehyde containing derivatives iswell known. Many of these modified polysaccharides have been used aspaper additives to improve properties such as strength, drainage andpigment retention- However, it has been found that the modifiedpolysaccharides are often not useful because they prematurely formcrosslinks and are not readily dispersible to provide desiredproperties.

The cationic polysaccharides can be produced by reaction with reagentswhich will introduce a cationic group containing nitrogen, sulfur orphosphorus therein as disclosed in "Cationic Starches" by D. B. Solarek,in Modified Starches: Properties and Uses, Chapter 8, 1986. Particularlyuseful cationic derivatives are the tertiary aminoalkyl starch ethersand the quaternary ammonium starch ethers.

Oxidative and non-oxidative methods have been used to introduce aldehydegroups into polysaccharides such as starches, gums and celluloses. Theoxidative methods used have included treatment with periodic acid,periodates, or alkali metal ferrates. See U.S. Pat. No. 3,086,969 issuedApr. 23, 1963 to J. E. Slager which discloses an improved process forthe preparation of a dialdehyde polysaccharide using periodic acid; U.S.Pat. No. 3,236,832 issued Feb. 22, 1966 to J. W. Opie et al. whichdiscloses a method of preparing periodate modified polygalactomannangums using periodic acid or the alkali metal salts thereof; U.S. Pat.No. 3,062,652 issued Nov. 6, 1962 to R. A. Jeffreys et al. whichdiscloses the preparation of dialdehyde gums using periodate or periodicacid; and U.S. Pat. No. 3,632,802 issued Jan. 4, 1972 to J. N. BeMilleret al. which discloses a method for oxidizing a carbohydrate (e.g.,starch or cellulose) with an alkali metal ferrate.

The disadvantages of the oxidative method include degradation to lowermolecular weight products and the formation of carboxyl groups due tofurther oxidation of the aldehyde groups. U.S. Pat. No. 3,553,193 issuedJan. 5, 1973 to D. H. LeRoy et al. describes a method for oxidizingstarch using an alkali metal bromite or hypobromite under carefullycontrolled conditions. The resulting aldehyde is reported to have asubstantially greater proportion of carbonyl groups, i.e., aldehydegroups, than carboxyl groups. It also discloses a method for selectivelyoxidizing the side chains of starch derivatives, e.g., an alkoxylatedstarch such as dihydroxypropyl starches, under the same processconditions whereby the underivatized starch hydroxy groups on the ringsare substantially non-oxidized.

The presence of carboxylic groups in aldehyde starches has severaldisadvantages in addition to the obvious reduction in the degree ofaldehyde substitution. This includes the introduction of hydrophilicproperties due to the carboxyl groups, an upset in the cationic/anionicratio when a cationic starch base is used (as in most papermaking wetend uses) and the possible formation of salts (in papermaking wet enduse) which could give rise to ionic crosslinking.

The non-oxidative methods typically involve the chemical modification ofthe polysaccharide with an aldehyde-containing reagent. Generally,chemical modification is random or not site-specific. See U.S. Pat. No.3,519,618 issued Jul. 7, 1970 to S. M. Parmerter and U.S. Pat. No.3,740,391 issued Jun. 19, 1973 to L. L. Williams et al. which coverstarch derivatives and U.S. Pat. No. 2,803,558 issued Aug. 20, 1957 toG. D. Fronmuller which covers a gum derivative. The starch derivative ofParmerter is prepared by reaction with an unsaturated aldehyde (e.g.,acrolein) and has the structure:

    Starch--O--CH(R.sup.1)--CH(R.sup.2)--CHO

where R¹ and R² are hydrogen, lower alkyls or halogen. The starchderivative of Williams is prepared by reaction with acrylamide followedby reaction with glyoxal and has the structure: ##STR1## The gumderivative of Fronmuller is prepared by treating the dry gum (e.g.,locust bean or guar gum) with peracetic acid to reduce the viscosity,neutralizing and then reacting with glyoxal. Water soluble celluloseethers (e.g., hydroxyethyl cellulose) have also been reacted withglyoxal or urea formaldehyde to give aldehyde-containing derivatives.

One of the disadvantages of introducing the aldehyde groups directlyusing an aldehyde-containing reagent is the possibility of thederivative crosslinking prior to use. This is a particular disadvantagewhen the products are being used to impart temporary wet strength topaper via a crosslinking reaction with the cellulose fibers. TheWilliams U.S. Pat. No. '391, cited above, alludes to this problem whenit notes that solutions of the glyoxalated polymers are stable for atleast a week when diluted to 10% solids by weight and adjusted to pH of3 (Col. 3, lines 60-63). The Parmerter patent notes that the starchaldehyde is a substantially non-crosslinked granular starch derivativeand discusses the importance of the non-crosslinked character (Col. 2,lines 40-45).

U.S. Pat. No. 4,675,394 issued Jun. 23, 1987 to D. B. Solarek et al.discloses a non-oxidative method for introducing block aldehyde groupsinto starch. This method avoids the premature reaction of the aldehydeby introducing acetal groups which are easily hydrolyzed at low pH toform the aldehyde. However, the generation of the aldehydic function atlow pH also degrades the polysaccharide backbone. For certainapplications, this degradation is undesirable. Cationic aldehydecontaining derivatives are further disclosed as being useful as paperstrength additives.

U.S. Pat. No. 3,297,604 issued Jan. 10, 1967 to F. J. Germino disclosesgalactose containing polysaccharides which are oxidized chemically orenzymatically with galactose oxidase. This patent further discloses theuse of these oxidized products as various intermediates for crosslinkingpolymers, both natural and synthetic, and for improving strengthproperties of cellulose and paper.

U.S. Pat. No. 4,031,307 issued Jun. 21, 1977 to R. N. De Martino et al.discloses cationic polygalactomannan compositions and more particularlya process for producing quaternary ammonium ethers of polygalactomannangums.

The composition of a cationic modified and site-specific oxidizednatural polysaccharide has not been disclosed previously and furthermoreit has now been found that surprising and unexpectedly improved paperstrength properties are achieved when using such polysaccharides asstrength additives.

SUMMARY OF THE INVENTION

The present invention provides aldehydic cationic derivatives ofgalactose containing polysaccharides which are obtained by oxidizing theselected polysaccharides with the enzyme galactose oxidase. The enzymeoxidized product has an aldehyde function at a specific position of thepolysaccharide, i.e., the C₆ --OH group of the galactose unit, and thecationic derivative thereof exhibits significantly improved andsurprising properties when used as a paper strength additive.

DETAILED DESCRIPTION OF THE INVENTION

The polysaccharides useful in preparing the aldehydic cationicderivatives of this invention are any of the galactose containingpolysaccharides and particularly the naturally occurring galactosecontaining polysaccharides. These are the polysaccharides containing thegalactose configuration at the C₄ position and which can be oxidized atthe C₆ --OH position to form an aldehyde group. Applicable galactosecontaining polysaccharides include polygalactomannan gums such as locustbean gum and guar gum, as well as tamarind gum and gum arabic. Thepolygalactomannan gums as noted above and used herein areheteropolysaccharides composed principally of long chains of mannoseunits and single unit side chains of galactose units and are furtherdisclosed in U.S. Pat. No. 4,276,414 issued on Jun. 30, 1981 to M.Tessler.

Guar gum is one of the polysaccharides which contain the galactoseconfiguration at the C₄ position and as illustrated below this galactoseconfiguration or unit is oxidized with the enzyme galactose oxidase toform an aldehyde group at a specific position of the unit, i.e., the C₆--OH group: ##STR2##

The aldehyde derivatives of galactose containing polysaccharides of thisinvention also contain one or more cation groups. Cationization of theselected polysaccharides can be produced by well known chemicalreactions with reagents containing amino, imino, ammonium, sulfonium orphosphonium groups as disclosed, for example in Solarek, "CationicStarches" supra and in U.S. Pat. No. 4,119,487 issued Oct. 10, 1978 toM. Tessler. Such cationic derivatives include those containing nitrogencontaining groups comprising primary, secondary, tertiary and quaternaryamines and sulfonium and phosphonium groups attached through eitherether or ester linkages. The preferred derivatives are those containingthe tertiary amino and quaternary ammonium ether groups.

The general method for preparing polysaccharides such as starchescontaining tertiary amine groups, which method typically involvesreacting starch under alkaline conditions with a dialkylaminoalkylhalide is described in U.S. Pat. No. 2,813,093 issued on Nov. 12, 1957to C. Caldwell et al. Another method therefore is disclosed in U.S. Pat.No. 4,675,394 issued Jan. 23, 1987 to D. Solarek et al. The primary andsecondary amine polysaccharides, e.g., starch, may be prepared byreacting the polysaccharide with aminoalkyl anhydrides, aminoalkylepoxides or halides, or the corresponding compounds containing aryl inaddition to the alkyl groups.

Quaternary ammonium groups may be introduced into the polysaccharide andstarch molecule by suitable treatment of the tertiary aminoalkyl etherof starch, as described in the previously noted U.S. Pat. No. 2,813,093.Alternatively, quaternary groups may be introduced directly into thepolysaccharide molecule by treatment with the reaction product of anepihalohydrin and a tertiary amine or tertiary amine salt, to providefor example, 3-(trimethylammonium chloride)-2-hydroxylpropyl ethersubstituent groups as disclosed in the noted U.S. Pat. No. 4,119,487.The above noted patents, i.e., U.S. Pat. Nos. '487, '093 and '394 areincorporated herein by reference as well as commonly assigned co-pendingU.S. patent application Ser. No. 07/376,779 filed Jul. 7, 1989 by Tsaiet al. which discloses other suitable cationic substituents. UsefulCationic derivatives include those containing amine or nitrogensubstituents having C₁ -C₆ alkyl groups, C₆ aryl or C₆ -C₁₂ alkarylgroups.

The preparation of cationic sulfonium derivatives is described in U.S.Pat. No. 2,989,520 issued June, 1961 to M. Rutenberg et al. andessentially involves the reaction of a polysaccharide in an aqueousalkaline medium with a beta-halogenoalkylsulfonium salt, vinylsulfoniumsalt or epoxyalkyl-sulfonium salt. The preparation of cationicphosphonium derivatives is disclosed in U.S. Pat. No. 3,077,469 issuedFeb. 12, 1963 to A. Aszalos and involves reaction of a polysaccharide inan aqueous alkaline medium with a beta-halogenoalkylphosphonium salt.

Other suitable cationic polysaccharides may be provided using reagentsand methods that are well known in the art as illustrated in the abovenoted references. Normally, the cation group is added to thepolysaccharide before forming the aldehyde because of the ease inhandling and preparation. If the aldehyde is formed first in the dryform, it is difficult to redisperse. The amount of cationic substituentson the polysaccharide can be varied and generally a degree ofsubstitution (D.S.) of from about 0.005 to 1.5 and preferably from about0.01 to 0.5 will be used. While larger amounts of cationic substituentsor higher degrees of substituents (D.S.) could be used, they are morecostly and difficult to make and therefore not economically attractive.The term "degree of substitution" (D.S.) as used herein is meant theaverage number of sites or substituent groups per anhydrohexose oranhydropentose units.

The polysaccharides useful as base materials, as described above, aregalactose containing polysaccharides that have the galactoseconfiguration in the C₄ position. When oxidized in accordance with thisinvention, using the enzyme galactose oxidase, an aldehyde is formed ata specific position of the polysaccharide, i.e., the C₆ -OH of thegalactose unit. The oxidation reaction is carried out by dispersing theselected polysaccharide in aqueous solution and then adding the enzymegalactose oxidase under an oxygen atmosphere. The reaction is allowed toproceed for a sufficient period of time to allow complete oxidation oruntil the desired degree of oxidation, i.e., aldehyde content, has beenattained. In carrying out the oxidation reaction of the galactosecontaining polysaccharide with the enzyme galactose oxidase, the rateand completeness of the reaction, like most enzyme catalytic reactions,are dependent on the concentration of the catalyst (as defined by theamount of active units) and substrate, as well as the temperature andpH. The aldehyde content is expressed in terms of dextrose equivalent(D.E.) which is the reducing value of the formed aldehyde derivative andis determined using the method described in Example II. The formedaldehyde derivative will preferably have a reducing value or aldehydecontent of at least 5 D.E. and more preferably at least 10 D.E. Themaximum D.E. value or aldehyde content will depend on the particularpolysaccharide base material that is used. For example, in the case ofguar gum which typically has a galactose/mannose ratio of about 38/62,the D.E. may approach 40 and in the case of other polysaccharides may beeven higher (see "Carbohydrate Research" by B. V. McCleary, 71, (1979)p. 216, for different polysaccharide galactose/mannose ratios).

The aldehyde cationic polysaccharide derivatives of this invention areuseful as paper additives particularly to improve dry and wet strengthand especially temporary wet strength properties. These aldehydecationic derivatives may be used as beater additives, although theiraddition to the pulp may occur at any point in the paper-making processprior to the ultimate conversion of the wet pulp into a dry web orsheet. Thus, for example they may be added to the pulp while the latteris in the hydropulper, beater, various stock chests or headbox. Thederivative may also be sprayed onto the wet web.

The aldehyde cation derivatives may effectively be used for addition topulp prepared from any type of cellulosic fibers, synthetic fibers, orcombination thereof. Among the cellulose materials which may be used arebleached and unbleached sulfite, bleached and unbleached soda, neutralsulfite, semi-chemical chemiground wood, ground wood or any combinationof these fibers. Fibers of the viscous rayon or regenerated cellulosetype may also be used, if desired.

Any desired inert mineral fillers may be added to the pulp which is tobe modified with the aldehyde cation derivatives herein. Such materialsinclude clay, titanium dioxide, talc, calcium carbonate, calcium sulfateand diatomaceous earths. Rosin or synthetic internal size may also bepresent, if desired.

The proportion of the aldehyde cation derivative to be incorporated intothe paper pulp may vary in accordance with the particular pulp involvedand the properties desired (e.g., wet strength, temporary wet strengthor dry strength). In general, it is preferred to use about 0.05 to 15%and more preferably about 0.1 to 5% of the derivative based on the dryweight of the pulp. Within the preferred range the precise amount whichis used will depend upon the type of pulp being used, the specificoperating conditions, the particular end use for which the paper isintended, and the particular property to be imparted. The use of amountsgreater than 5% is not precluded, but is ordinarily unnecessary in orderto achieve the desired results.

The following examples will more fully illustrate the embodiments ofthis invention. In the examples, all parts and percentages are by weightand all temperatures in degrees Celsius unless otherwise noted.

EXAMPLE I

This example describes the preparation of cationic derivatives ofgalactose containing polysaccharides, i.e., guar gum, tamarind gum andlocust bean gum.

One hundred (100) g (dry basis) of guar gum was slurried into 285 ml. ofisopropanol and 3 g of sodium hydroxide along with I g of boraxdissolved in 80 ml H₂ O was added to the slurry. While under goodagitation, 5 g of 3-chloro-1-hydroxypropyl-trimethylammonium chloride(Dow Quat 188) was added to the slurry and the mixture was allowed toreact at 40° C. for 16 hours under nitrogen atmosphere. The mixture wasthen neutralized with hydrochloric acid (18% in isopropanol) to a pH of8, filtered and washed three times with 80% aqueous isopropanol. Thesample was then air dried and used for the galactose oxidase treatmentprocedure in Example II. Additional samples of de-oiled tamarind gum andlocust bean gum were prepared using the same procedure described above.

EXAMPLE II

Galactose oxidase treated cationic gums were prepared in the followingmanner.

Ten (10) g of cationic guar gum prepared in Example I was added slowlyalong with 1 g of preservative Dowcide A to 1 liter of deionized waterunder good agitation. The pH of the dispersion was adjusted to 3 byadding phosphoric acid, held for about 30 minutes and then readjusted to7. The mixture was then heated in a boiling water bath for one hour,cooled to room temperature followed by the addition of galactose oxidase(2500 units) obtained from Sigma Chemical Co. (one unit has activity ofΔA₄₂₅ of 1.0 per minute at pH 6.0 in 25° C., in a peroxidase ando-tolidine system) and catalase (250,000units) obtained from SigmaChemical Co. (one unit will decompose 1.0μ mole of H₂ O₂ per minute atpH 7.0 at 25° C. while the H₂ O₂ concentration falls from 10.3 to 9.2mM) to remove H₂ O₂ which is generated during the reaction. The reactionwas allowed to proceed under oxygen atmosphere until a desirablealdehyde content (degree of oxidation) was achieved. The aldehydecontent was determined and expressed as dextrose equivalent (D.E.) bythe method described below. The reaction was stopped by deactivating theenzyme in a boiling water bath for 30 minutes.

Samples of the cationic tamarind gum and locust bean gum prepared inExample I were also tested with galactose oxidase in the same manner.

The following procedure adopted from M. Macleod and R. Robson Biochem J.23, 517(1929)! with modification was used to estimate the reducing value(aldehyde content) of the galactose oxidase treated cationic gums.

A standard curve for dextrose was prepared by titrating 1, 5, and 10 mgsamples of dextrose.

A known amount of dextrose was added to a 50 cc solution of 1.58×10⁻³ MI₂, 1.87×10⁻¹ M KI and 3.74×10⁻³ M KCl followed by 10 cc of 6.1×10⁻⁴ Msodium carbonate solution. The mixture was brought to a total volume of110 cc under good stirring for one hour. Ten (10) cc of 1N HmSO₄ wasadded and the solution titrated with 0.005N sodium carbonate stabilizedsodium thiosulfate solution using three drops of 1% solubilized starchsolution as indicator.

For experimental samples, 20 mg of the galactose oxidase treated gumswas used and the reducing value of the formed aldehyde was determined asdextrose equivalent (D.E.) by calculating the equivalent of iodineconsumed with reference to the standard dextrose curve. The resultsshown as aldehyde content (D.E.) are shown in the table found in thenext example (Example III).

EXAMPLE III

This example describes and compares the use of the aldehyde, cationicderivatives of galactose containing polysaccharides of this invention aspaper strength additives.

Paper hand sheets containing the test and control additives wereprepared in the following manner. To a headbox containing 12 liters ofwater (pH 7), 1.2 g of northern softwood kraft fiber (640 CSF--CanadianStandard Freehess) dispersed in 400 cc of water was added. Under goodagitation, the additive was added at 10 lb/ton of fibers at 0.5%concentration (w/w). The mixture was drained through a 94 mesh papermachine wire, the wet sheet then put between blotters and predried in aNoble & Wood drum dryer. The blotters were removed and the sheet curedin an oven at 105° C. for 30 minutes. Before testing for strengthperformance, the sheet was preconditioned in a constant temperature roomwith 50% relative humidity for at least two hours.

In the paper tests, the tensile strengths are reported as breakinglength (m.). The breaking length is the calculated limiting length of astrip of uniform width, beyond which, if such a strip were suspended byone end, it would break of its own weight. The breaking length (air dry)in meters (m.) is calculated using the formula B.L.=102,000 T/R=3,658T'/R', where T is tensile strength in kN./m., T' is tensile strength inlb./in., R is grammage (air dry) in g./m.², and R' is weight per unitarea (air dry in lb./1000 ft.²). Paper specimens are selected inaccordance with TAPPI T 400 sampling procedure. Those evaluated for wetstrength and temporary wet strength were saturated with distilled waterby immersion and/or soaking until the paper sample was thoroughlywetted. The strength was evaluated in accordance with TAPPI T 494 om-82.The measurements were carried out using a constant rate of elongationapparatus, i.e., a Finch wet strength device which is described in TAPPIProcedure T 456 om-82 (1982). The dry strength was evaluated inaccordance with TAPPI T 494 om-81.

The table below illustrates the paper strength improvement obtained byusing the galactose oxidase treated cationic guar gum.

    ______________________________________                                                           Paper Strength**                                                                          Wet Tensile                                                Aldehyde*                                                                              Dry Tensile                                                                             (5 sec)                                                    Content (D.E.)                                                                         (B.L. - m)                                                                              (B.L. - m)                                     ______________________________________                                        1)  Unmodified guar gum                                                                         0          1825    45                                       2)  Guar gum treated with                                                         Dow Quat. 188                                                                 2.5%          0          1709    45                                           5.0%          0          1738    47                                       3)  Unmodified guar gum                                                                         13.5       1856    246                                          treated with                                                                  galactose oxidase                                                         4)  Guar gum treated with                                                                       10.5       2377    397                                          5% Dow Quat. and                                                              galactose oxidase                                                         ______________________________________                                         *Aldehyde content expressed as dextrose equivalent (D.E.) and determined      by iodometric method using glucose as reference standard = 100                **Addition level of gum: 10 lbs/ton of pulp                              

The results show that paper strength was not improved using cationmodification alone and only the wet strength was improved with galactoseoxidase treatment. However, using both cationic modification andgalactose oxidase treatment both the wet and dry strengths weresignificantly improved.

EXAMPLE IV

This example illustrates the use of galactose oxidase treated cationicde-oiled tamarind gum as a paper strength additive following the sameprocedure described in Example III.

    ______________________________________                                                           Paper Strength                                                                            Wet Tensile                                                Aldehyde*                                                                              Dry Tensile                                                                             (5 sec)                                                    Content (D.E.)                                                                         (B.L. - m)                                                                              (B.L. - m)                                     ______________________________________                                        1)  De-oiled tamarind gum                                                                       0          1586    38                                       2)  De-oiled tamarind gum                                                                       0          1676    37                                           treated with 5% Dow                                                           Quat.                                                                     3)  De-oiled tamarind gum                                                                       10.8       1563    116                                          treated with                                                                  galactose oxidase                                                         4)  De-oiled tamarind gum                                                                       9.4        1720    218                                          treated with 5% Dow                                                           Quat. and galactose                                                           oxidase                                                                   5)  Purified tamarind gum                                                                       15.7       2044    265                                          (Glyloid 3S) treated                                                          with 5% Dow Quat.                                                             and galactose oxidase                                                     ______________________________________                                    

The results show the significant improvement in both wet and drystrength that is obtained when using the tamarind gum having bothcationic modification and galactose oxidase treatment.

EXAMPLE V

This example illustrates the effectiveness of galactose oxidase treatedcationic locust bean gum as a paper strength additive. The sameprocedure described in Example III was followed.

    ______________________________________                                                           Paper Strength                                                                            Wet Tensile                                                Aldehyde*                                                                              Dry Tensile                                                                             (5 sec)                                                    Content (D.E.)                                                                         (B.L. - m)                                                                              (B.L. - m)                                     ______________________________________                                        1)  Unmodified locust                                                                           --         1688    43                                           bean gum                                                                  2)  Locust bean gum treat-                                                                      --         1704    41                                           ed with 5% Dow Quat.                                                      3)  Locust bean gum treat-                                                                       8.8       1816    224                                          ed with 5% Dow Quat.                                                                        11.9       2041    274                                          and galactose oxidase                                                                       13.9       1925    305                                      ______________________________________                                    

The results show the significant improvement in both wet and drystrength that is obtained when using the locust bean gum having bothcationic modification and galactose oxidase treatment.

What is claimed is:
 1. An aldehyde cationic polysaccharide derivativewherein the polysaccharide is a naturally occurring galactose containingpolysaccharide which is cationized by etherification or esterificationreactions and subsequently oxidized by reacting with galactose oxidaseto provide an aldehyde group in the C₆ position of the galactose unit ofthe naturally occurring galactose containing polysaccharide moiety andwherein the aldehyde cationic polysaccharide derivative has a cationiccontent represented by a DS of from about 0.005 to 1.5 and an aldehydecontent represented by a DE of at least
 5. 2. The polysaccharidederivative of claim 1 wherein the polysaccharide is selected from thegroup consisting of guar gum, locust bean gum, tarmarind gum and gumarabic.
 3. The polysaccharide derivative of claim 2 having a cationiccontent represented by a D.S. of from about 0.01 to 0.5 and an aldehydecontent represented by a D.E. of from about 5 to
 40. 4. Thepolysaccharide derivative of claim 3 which contains tertiary alkyl oraryl amine or quaternary alkyl or aryl ammonium ether cationic groups.5. The polysaccharide derivative of claim 4 wherein the cationic groupsare diethylaminoethyl ether groups or 3-(trimethylammoniumchloride)2-hydroxypropyl ether groups.
 6. The method of preparing thepolysaccharide derivative of claim 1 which comprises the steps of:(a)dispersing a cation containing polysaccharide derivative in water, saidderivative being a galactose containing polysaccharide; and (b)oxidizing the cation, polysaccharide derivative by reacting withgalactose oxidase to provide an aldehyde group in the C₆ position of thegalactose unit.
 7. The method of claim 6 wherein the polysaccharide isselected from the group consisting of guar gum, locust bean gum,tamarind gum and gum arabic and contains tertiary alkyl or aryl amine orquaternary alkyl or aryl ammonium ether cationic groups.